In elevator systems, passengers ride in a car comprising a cab which is suspended on a frame to which the car lifting equipment is attached. Many elevator cabs have a rigid, sturdy frame to which decorative panels, functioning solely as walls, are attached in order to provide a passenger enclosure. The cab rigidity of cabs constructed this way is primarily a function of the rigidity of the frame, not the walls. Also, cabs constructed this way are generally expensive and typically heavy, mainly due to the use of a heavy frame in order to give the cab rigidity. A heavy cab, of course, requires larger elevator components, most significantly a more powerful elevator drive, which thus also wastes more energy than a lower power motor. Drive power also limits acceleration. And, in hydraulic elevators the weight is even more critical since there is no regeneration to speak of. Hence, by achieving a substantial reduction in the cab weight, it becomes possible to reduce excess mass in the system by reducing both the number of ropes in the system and the counterweight mass, and thereby provide a lower cost, energy efficient elevator.
Other cab construction approaches are found in the prior art, and these have focused mainly on reducing the cost of the cab, or aesthetic appeal, not necessarily weight. Generally speaking, prior art cab design criteria have focused on cost reduction, underestimating, if not ignoring, the negative effects from excess system mass, which is present when a cab is heavier than it has to be. One, using a modified "monoque" construction similar to that used in constructing automobiles, uses steel panels which are clipped together. According to another technique described in British Patent Specification No. 1,493,610, the ceiling portion of the cab is reenforced in order to make the ceiling strong enough to support the cab load.